Analysis by: Christopher Daniel So
ALIASES:

Virus:Win32/Virut.BN (Microsoft); W32.Rontokbro@mm (Symantec); W32/Virut.n.gen (McAfee); Virus.Win32.Virut.ce (Kaspersky); Virus.Win32.Virut.ce (Sunbelt)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This worm arrives as attachment to mass-mailed email messages.

It disables Task Manager, Registry Editor, and Folder Options.

  TECHNICAL DETAILS

File Size: 127,488 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 10 Feb 2011

Arrival Details

This worm arrives as attachment to mass-mailed email messages.

Installation

This worm drops the following copies of itself into the affected system:

  • %Application Data%\csrss.exe
  • %Application Data%\inetinfo.exe
  • %Application Data%\lsass.exe
  • %Application Data%\services.exe
  • %Application Data%\smss.exe
  • %Application Data%\winlogon.exe
  • %System%\{user name}'s Settings.scr
  • %User Profile%\Templates\Brengkolang.com
  • %Windows%\eksplorasi.exe
  • %Windows%\ShellNew\sempalong.exe

Autostart Technique

This worm adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
WIndows\CurrentVersion\Run
Tok-Cirrhatus = "%Application Data%\smss.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "Explorer.exe %Windows%\explorasi.exe"

(Note: The default value data of the said registry entry is "Explorer.exe".)

It drops the following file(s) in the Windows User Startup folder to enable its automatic execution at every system startup:

  • %User Startup%\Empty.pif

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

Other System Modifications

This worm creates the following registry entry(ies) to disable Task Manager, Registry Tools and Folder Options:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 1

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableCMD = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer
NoFolderOptions = 1

Other Details

This worm does the following:

  • Propagates by sending a copy of itself as an attachment to email messages

NOTES:
This wom is infected with PE_VIRUX.R.

  SOLUTION

Minimum Scan Engine: 8.900
VSAPI PATTERN File: 7.832.04
VSAPI PATTERN Date: 12 Feb 2011
VSAPI PATTERN Date: 2/12/2011 12:00:00 AM

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Remove the malware/grayware file dropped/downloaded by WORM_BRONTOK.VRX. (Note: Please skip this step if the threat(s) listed below have already been removed.)

Step 3

Terminate a malware/grayware process

[ Learn More ]

*Note: If the detected process is not displayed in theWindows Task Manager, continue doing the next steps.

    • %Application Data%\csrss.exe
    • %Application Data%\inetinfo.exe
    • %Application Data%\lsass.exe
    • %Application Data%\services.exe
    • %Application Data%\smss.exe
    • %Application Data%\winlogon.exe
    • %Windows%\eksplorasi.exe

Step 4

To enable Registry Editor, Task Manager, and Folder options:

  1. Open Notepad. To do this:
    • For Windows 2000, XP, and Server 2003 users:
      Click Start > Run, type Notepad in the text box provided, then press Enter.
    • For Windows Vista and 7 users:
      Click Start > type NotepadREGEDIT4
      [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
      DisableRegistryTools=-
      [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
      DisableCMD=-
      [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
      NoFolderOptions=-
      [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon]
      Shell=explorer.exe, then press Enter.
  2. Copy and paste the following script:
  3. Save this file asREGEDIT4
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableRegistryTools=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableCMD=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
    NoFolderOptions=-
    [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon]
    Shell=explorer.exeREGEDIT4
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableRegistryTools=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableCMD=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
    NoFolderOptions=-
    [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon]
    Shell=explorer.exeC:RESTORE.VBS.
  4. Click Start>Run again, type C:RESTORE.VBS in the text box provided, then press Enter.
  5. Click Yes at theREGEDIT4
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableRegistryTools=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableCMD=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
    NoFolderOptions=-
    [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon]
    Shell=explorer.exeREGEDIT4
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableRegistryTools=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
    DisableCMD=-
    [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
    NoFolderOptions=-
    [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon]
    Shell=explorer.exeprompt of the message box to execute the .VBS file.

Step 5

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Tok-Cirrhatus=%Application Data%\smss.exe

Step 6

Scan your computer with your Trend Micro product to delete files detected as WORM_BRONTOK.VRX. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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